Numerical investigation of the seismic response of a UHV composite bypass switch retrofitted with wire rope isolators

An ultra-high voltage (UHV) composite bypass switch (BPS) faces increasing seismic challenges when UHV projects extend to high seismic intensity areas. The UHV composite BPS still generates excessive stress at the bottom section although hollow composite insulators with high flexural strength are adopted. Since the standard retrofitting strategy by using stiffer supports cannot reduce stress responses, wire rope isolation is introduced. The optimal design of isolation considers both stress and displacement responses since the slenderness and composite material of insulators contribute to significant displacement. The results show that properly designed isolation can significantly reduce stress without excessive displacement responses. A larger radius configuration helps to improve the applicability of small stiffness isolators under high winds. When the isolation still cannot satisfy the requirement, smaller stiffness isolators with a larger radius, or isolators with increased loops and smaller radius, can be introduced to gain better energy dissipation capacity and effectiveness in response mitigation. Accordingly, a three-step design procedure is proposed to increase the damping force but fix the rotational stiffness of isolation. Hence, the application of wire rope isolation can be extended to UHV composite BPS with a low natural frequency, but conductors with enough redundancy should be used.